Wind deflectors, side wings, bikini tops, and doors

Wind wings, doors, wind deflectors, bikini tops, hard tops, anything to manage wind buffeting. Aerodynamics has its own forum.
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Midlana1
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Wind deflectors, side wings, bikini tops, and doors

Post by Midlana1 » 26 Jun 2013, 09:12

Figured I may as well start dumping links to useful information into a common thread to hash this out.

First, meet the enemy:

Image

As can be seen, and confirmed through my own and others' experiences, the wind coming over the top of the glass isn't the problem, it's that it whips around the sides. Imagine getting hit in the ear by a pillow a thousand during a drive, that's what it's like. Earplugs work but not as much as expected since the low-frequency wind "thumping" goes right through them, never mind the physical "hits" that your body takes. Then there's wearing a baseball hat, that no matter how tightly-adjusted, is threatening to leap off at anything above 60 mph. Even more striking is when passing - or being passed by - a large vehicle, where the "bow wave" of air pushed in front of them can increase the turbulence to something pretty unpleasent.

Useful links:
http://www.locostusa.com/forums/viewtop ... 23&t=13288
http://www.locostusa.com/forums/viewtop ... 23&t=12170
http://www.locostusa.com/forums/viewtop ... f=4&t=8044
http://www.locostbuilders.co.uk/viewthr ... tid=156995
http://usa7s.com/vb/showthread.php?p=74641
http://www.locostusa.com/forums/viewtop ... 23&t=13379

McMaster lift-off hinges http://www.mcmaster.com/#catalog/119/2956/=nd1bxs


Doing a lot of reading, it appears that doors, or large side wind deflectors, really go a long way to minimizing the turbulence which whips around the side of the windscreen.

More later...

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Re: Wind deflectors, side wings, bikini tops, and doors

Post by goochie » 23 Aug 2016, 16:07

I'm interested in this having had a discussion with another engineer earlier in the week. He has previously worked for a couple of low volume car manufacturers in Europe and is now a CAD systems specialist here in Australia.

The conversation started out around the ability for our Solidworks Licence to carry out CFD which, turns out it cant. However he pointed me toward a free open-source program called Open Foam http://www.openfoam.com/ which apparently compares very well against more expensive alternatives for simply projects like this.

I discussed the theory that the wind disturbance is caused by the air entering the sides of the cabin and he says he think's that is wrong. In his experience it is much more likely to be caused by the open space behind the seats. The key is apparently to create a pocket of trapped air within the cabin that will resist the air that's trying to come in through the sides.

This is along the lines of many Locost builders in the links posted above and is why so many open top sports cars have a small screen between the headrests and why there is a small industry making aftermarket wind deflectors. If you do a Google image search you'll see many examples: https://www.google.com.au/search?q=conv ... gQ_AUIBygC

This youtube video demonstrates the wind deflector benefits nicely: https://www.youtube.com/watch?v=ix1rkdI5cR0

So my question to those who have finished their Midlana - Have you experimented with putting something in the space behind the seats?

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Re: Wind deflectors, side wings, bikini tops, and doors

Post by Midlana1 » 23 Aug 2016, 19:12

I agree with your friend, in a roundabout way. That is, the wind does whip in from the sides - think of a kid repeatedly whacking you in the side of the head with a pillow, which is hard on the ears. I think the reason it whips in from the sides is because of the low pressure generated by the wind up over the top of the windscreen, which also sucks air forward from the rear. Blocking the rear flow with a screen behind the seats should reduce it, as well as some sort of roof panel. Looks like I'll be finding out soon since I've decided to go with a scoop at the top edge of the windscreen.

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Re: Wind deflectors, side wings, bikini tops, and doors

Post by ChrisS » 24 Aug 2016, 00:05

I can't offer any theory, just some personal experiences from a few open top cars. First is the Westfield. This has the usual flat screen and we only ever drove it once without the side screens on, it was truly awful. Buffeting so bad my specs came off when we hit 30mph. Side screens that are as high as the screen and extend to just behind my shoulders make it entirely comfortable up to about 90, after which speed you tend to lose your baseball cap.

Next was a cobra replica. Taller, curved screen and you sit a bit lower. Buffeting was fairly bad but bearable at normal speeds, after fitting some 'wind wings' it was massively improved.

A Marcos Mantula Spyder. Screen about the same relative height as the cobra, nicely curved, proper doors with moving glass. All that used to give was a bit of the reverse buffet at illegal on the road speeds. Otherwise it was a nice experience.

I'll be starting off with some 'wind wings' on my Midlana and see how that works. A rear net sounds like it'll be worth experimenting with too, although the Westfield community here don't seem to rate their effectiveness that highly.
Midlana No.2

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Re: Wind deflectors, side wings, bikini tops, and doors

Post by Midlana1 » 24 Aug 2016, 06:12

My Mini had a curved Mini windscreen and slider windows, but being mid-engine meant that there was a bulkhead behind me. Wind would come in the slider windows, hit the bulkhead and make a hard turn straight into my ear. While the wind wasn't nearly as bad as Midlana*, it showed that having a divider is a mixed blessing; I'm not sure what it'll do on Midlana but it's an easy test.

*Locosts have the same issue due to their similar shape.

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